The present invention is directed to an aqueous emulsion prepared from a solid and liquid organic peroxide, an aqueous size containing the emulsion, and sized glass fibers. More particularly, the present invention is directed to an aqueous peroxide emulsion made from a solid and liquid organic peroxide, aqueous size containing same, and sized glass fibers prepared for bonding to polymers in the reinforcement of polymeric materials.
Organic peroxides that decompose by initial cleavage of the oxygen-oxygen bond to produce free radicals act as initiators for vinyl monomers and other vinyl-containing and diene-containing materials. There are over fifty different organic peroxides classified into nine major types that are used commercially in the polymer and resin industries. The half-life (T.sub.1/2) of various peroxides, which is given as a function of temperature can range from around 0.01 hours at elevated temperatures to as long as 1,000 hours at lower temperatures for the more stable peroxides. The half-life is a measure of the thermal stability of organic peroxides by measuring the time for decomposition of 50 percent of the original amount of peroxide, which is a half-life for a first-order reaction. These organic peroxides have been used in the polymerization of vinyl monomers and diene monomers and polymers to produce bulk polymers, polymer films and other polymer compositions.
Depending on the thermal stability and other physical characteristics of the particular peroxides, various organic peroxides can be used or transported in different forms when they are to act as initiators or curing agents for vinyl polymerization. Some of the organic peroxides such as the highly reactive percarbonates are so unstable that they must be shipped as a frozen solid or an undiluted liquid under refrigeration. Some less reactive organic peroxides, such as lauroyl peroxide and dibenzoyl peroxide are more stable at room temperature and can be cured with greater facility and with less stringent precautions. For example, the relatively more stable benzoyl peroxide, which is a solid at room temperature having a melting point of 106.degree. to 107.degree. C. can be used as granules or cystals or in a thick paste compounded with a phlegmatiser such as tricresyl phosphate. Also, benzoyl peroxide can be used in aqueous solution as is shown in U.S. Pat. No. 2,343,084 (Smith), wherein the small amount of benzoyl peroxide is dissolved in one or more polymerizable conjugated compounds and may also contain a resin in solution. This solution can be combined with a water solution of a partially saponified polyvinyl acetate. Also, it has been suggested in U.S. Pat. No. 3,795,630 (Jaspers et al) to have a chemically stable non-separating organic peroxide composition of an organic peroxide which is a solid at room temperature. The composition is obtained by mixing the solid peroxide like benzoyl peroxide with a liquid phlegmatiser like phthalate plasticizers or epoxidized soya bean oil and glycols, along with a hydrophobic alkyl group containing silica. In addition, it is shown in U.S. Pat. No. 4,039,475 (Jannes) to have a stable, pumpable aqueous suspension or organic peroxides containing one nonionic emulsifier having a maximum HLB value of 12.5 and another nonionic emulsifier having a minimum HLB of 12.5 or a second emulsifier that is anionic.
Organic peroxides such as the aryl alkyl peroxide, dicumyl peroxide; ester peroxides and aromatic and aliphatic acyl peroxides have been used in compositions for sizing fibrous materials for use in polymer applications as shown in U.S. Pat. No. 3,013,915 (Morgan). These peroxides which have low volatilities and low decomposition points usually below about 180.degree. F. (82.degree. C.) are deposited on the fibers from an organic solution. In the composition along with the organic peroxide there is present a suitable coupling agent.
It is also known as is shown in U.S. Pat. No. 3,837,898 (McCombs et al) to form a polybutadiene emulsion that contains heat activated curing agents to operate as a catalyst in the size coating on fibers. The curing agents are the well-known free radical catalysts such as organic peroxides, e.g., benzoyl peroxide, lauroyl peroxide, tert-butyldiethyl peracetate, diacetyl peroxide, as well as inorganic peroxides, and redox catalysts such as potassium persulfate. The polybutadiene emulsion is prepared by mixing the polybutadiene with an emulsifying agent and with benzoyl peroxide. To this mixture there is added sufficient water to form an emulsion of the liquid polymer in aqueous medium. The emulsion is then mixed with a mixture of water, glass fiber anchoring agents and a gel agent and the resulting composition is homogenized to form a sizing composition having a solids content of about 2.80 and a pH of about 10.0 to 10.5. The emulsifying agents that can be used are any conventional emulsifying agents, but preferably are the nonionic emulsifying agents such as the polyoxyethylene derivatives of fatty acid, partial esters of sorbitol anhydrides, or the polyoxyethylene derivatives of fatty alcohols, or of the alkyl substituted phenols.
It was recently suggested in U.S. Pat. No. 3,849,148 (Temple) to prepare an aqueous size for glass fibers to be used in reinforcing polyolefin materials wherein the size contained a coupling agent, a heat stable organic peroxide, a nonionic surfactant and usually a lubricant or softener, and optionally a film-former. The heat stable organic peroxide includes organic peroxides having peak decomposition temperatures above about 200.degree. F., (93.3.degree. C.) for example, alpha alpha' bis(t-butylperoxy)-diisopropl benzene, tris(t-butylperoxy)-diisopropyl benzene, 2,5(t-butylperoxy)hexane, and 2,5(t-butylperoxy)hexyne. These heat stable peroxides are used in emulsions with nonionic surfactants such as polyethoxy phenols and are prepared and dispersed in water containing a coupling agent. Emulsions prepared at temperatures in the range of 120.degree. F. (49.degree. C.) to 210.degree. F. (99.degree. C.) including issoctyl phenyl polyethoxy ethanol are particularly useful. Other useful nonionic surfactants belonging to the class of polyethoxy phenols are nonyl polyethoxy ethanol and alkyl etherpolyethoxy ethanol. Other nonionic surfactants which are useful are polyalkylene glycol ethers, alkyl polyether alcohol and alkyl aryl polyether alcohol. The emulsion is prepared by thoroughly mixing the radical peroxide initiator with the nonionic surfactant maintaining the temperature of the mixture above the melting point of the free radical initiator. Suitable temperature control is possible by immersing the mixing vessel in boiling water. After thoroughly mixing the free radical peroxide initiator with nonionic surfactant, water is slowly added to the mixture at a temperature above the melting point of the free radical initiator, preferably in the range of about 140.degree. F. (60.degree. C.) to 150.degree. F. (66.degree. C.) until the emulsion inverts. The emulsion is then slowly cooled to ambient conditions by continued water addition. This emulsion is then slowly added to the aqueous mixture containing the coupling agent and the remaining water is added to the mixture to form an aqueous sizing composition for treating glass fibers.
In forming an emulsion for use in a sizing composition for glass fibers, it is necessary to obtain an emulsion that has shear stability, shelf stability and process stability and preferably that has a small particle size. It is necessary to have an emulsion rather than a suspension because of the particle size limitation. An emulsion is a two-phase system consisting of two incompletely miscible liquids, the one liquid being dispersed as fine droplets in the other liquid. A suspension is a two-phase system closely related to an emulsion, in which the dispersed phase is a solid. The stability of an emulsion depends upon such factors as particle size; difference between the density of the dispersed, discontinuous or internal phase that is the liquid broken-up into droplets and the density of the continuous or external phase which is the surrounding liquid; the viscosity of the continuous phase in the emulsion; the charges on the particles; the nature, effectiveness and amount of emulsifier used; and the conditions of storage, including the temperatures of storage, agitation and vibration and dilution or evaporation during the storage or use.
The particle size or particle size distribution of the emulsion are controlled by such factors as the quantity or the efficiency of the emulsifier, the order of mixing, and the agitation employed. The average particle size or particle size distribution of the emulsion is an important factor since large liquid particles in the emulsion or for that matter, particles of solid material as in a suspension would not provide an adequate uniform coating to the glass fibers. Solid particles would abraid the glass fibers and large liquid particles would cover the surface of the glass fiber in a spotty fashion leaving hiatuses in the coating along the fibers that as a result would not adequately contact the matrix resin to be reinforced.
The emulsion used in a sizing composition for glass fibers must be of sufficient dilution to approach a water thin liquid in order to facilitate application of the sizing composition to the glass fibers during formation of the fibers. Dilution of an emulsion, especially dilution to the extent of a water-thin-liquid can lead to an unstable emulsion. Also, the emulsion must be shear stable to withstand the mixing of the sizing composition before being applied to the glass fibers, and it must be shelf stable for periods of three days to more than a week so that the material may be stored before application to the glass fibers. Also, the emulsion must be process stable to enable the size to be applied to the fibers.
A problem that has recently surfaced with the use of some heat stable, solid organic peroxides is that, when used in an emulsion, which is formed at a temperature above the melting point of the peroxide but which is used at a temperature below the melting point of the peroxide, the emulsion tends to have particle sedimentation or creaming. An additional problem with organic peroxides that are solid at 20.degree. C. and have a melting point and a decomposition temperature at an elevated temperature is the chance of a violent decomposition reaction during the attempt to melt the peroxide in the course of emulsification.
It is an object of the present invention to provide an emulsion of a solid, organic peroxide that has a melting point and decomposition temperature at an elevated temperature where the emulsion can be formed at a temperature below the melting point of the solid-organic peroxide and can be diluted to have a viscosity approaching the viscosity of water and that has improved shear stability, shelf stability, and process stability.
It is an additional object of the present invention to provide an emulsion of a heat-stable organic peroxide that can be used in a sizing composition for glass fibers where the emulsion is shear stable, shelf stable and process stable within the sizing composition.
It is a further additional object of the present invention to provide processes for preparing an emulsion of a heat-stable organic peroxide and a sizing composition containing same that has improved dilutability, that is shear stable, shelf stable, and process stable and that has good average particle size and particle size distribution.
It is another further object of the present invention to provide sized glass fiber strands having fibers in the strand with a coating of an aqueous sizing composition containing a coupling agent, an emulsion of heat stable organic peroxide that has improved dilutability, improved shear stability, shelf stability, and process stability, and a good particle size distribution and good average particle size and usually a lubricant or softener and optionally a film-former.